In displaying an image on an LCD, distortion of the image may occur which is dependent on the pattern of the image, e.g., the intensity of particular regions of the image with respect to other regions of the image. This image-dependent distortion may be caused by a phenomenon known as "cross-talk."
A typical LCD 5 is depicted in FIG. 1. The LCD 5 may include first and second substrates 10, 20, which are connected to a printed circuit board 30 which is mounted adjacent a side edge and upper and lowers edges of the first and second substrate 10. A plurality of data line driver integrated circuit packages 40, 42 typically connect the printed circuit board 30 to upper and lower edges of the second substrate 20, and drive a plurality of data lines formed on the second substrate 20. A plurality of gate driver IC packages 60 typically connect the printed circuit board to the side edge of the second substrate 20, and drive a plurality of gate lines formed on the second substrate 20.
Typically, a common electrode layer 9 is typically formed on the first substrate 10, substantially covering the surface of the first substrate 10 as illustrated in FIG. 2, which serves as a common electrode for the liquid crystal elements of the display 5. A data line driver IC package 40 includes a tape automated bonding (TAB) tape 50 which includes a plurality of conductors which are connected to a plurality of data lines on the second substrate 20. A data driver IC 52 is mounted on the bonding tape 50 and is electrically connected to the plurality of conductors in the bonding tape 50, thereby connecting the data line driver IC 52 to a group of data lines on the second substrate 20. These data lines may be connected directly to electrodes of liquid crystal elements (passive LCD) or indirectly connected to electrodes of liquid crystal elements through control elements such as thin-film transistors (TFTs), as is well-known to those skilled in the art. The bonding tape 50 also may include common electrode conductors 51 which are connected to the common electrode layer 9. These common electrode conductors 51 are typically connected to the output of an common electrode driver 54, typically a voltage follower operational amplifier circuit, through a trace of the printed circuit board 30. The common electrode driver 54 circuit drives the common electrode layer 9 with a common electrode voltage through the common electrode conductors 51.
Referring again to FIG. 1, when the display 5 attempts to display a black region 70 surrounded by white, for example, cross-talk can cause the white regions to have differing intensities. The white regions 82 above and below the black region 70 may appear darker than the white regions 80 on either side of the black region 70. This distortion may be attributed to a distortion of the common electrode voltage on the common electrode layer 9 with respect to the other control signals applied to the LCD 5, e.g., the data signals applied to individual LCD elements.
FIG. 3 illustrates an ideal common electrode voltage 3 with respect to a gate drive signal 1 and a video voltage 2 which corresponds to a "black" level for a "normally white" liquid crystal element. As shown, the common electrode voltage 3 ideally has an inverted phase with respect to the video voltage 2, thus producing a maximum voltage A across the liquid crystal element. However, as illustrated in FIG. 4, the actual common electrode voltage 4 may be delayed with respect to the video voltage 2, thus producing a reduced voltage B across the liquid crystal element. This delay may be caused by the impedance characteristics of the common electrode layer 9. As illustrated in FIG. 5, when "white" is displayed, the video voltage 2 is ideally in phase with the common electrode voltage, thus producing a minimum voltage D across the liquid crystal element. As with black display of FIG. 4, the actual common electrode voltage 4 may be distorted due to impedance characteristics of the common electrode.
However, the common electrode voltage can be further distorted for "white" elements adjacent elements which are displaying "black." Cross-talk may occur because increased discharge currents from the "black elements" may locally reduce the common electrode voltage magnitude and thus the voltage difference between the common electrode and the video voltage of the adjacent "white" elements. This reduced voltage may cause "white" elements adjacent "black" elements to appear brighter than "white" elements in other portions of the display. This effect can be exacerbated in white regions horizontally adjacent a black region for a common electrode structure such as that illustrated in FIGS. 1 and 2.